Because of difficulties in finding forestry successors and falling in timber price, forest management has become more and more difficult, which brings about a serious problem of deserted forests. Although tree thinning and pruning are main procedures in forest management, timbers from thinning and branches and leaves cut off thereby are not only economically valueless but require an additional cost. Therefore, it is no surprise that these management procedures are neglected.
Under these circumstances, attempts have been made in these years to process wood materials obtained by tree thinning and so on to thereby provide useful resources. For example, timbers from thinning are chipped, cooked and then used as animal feeds.
However, the aforesaid method requires large equipment for chipping and cooking and, therefore, is not easily available anywhere. Setting timbers aside, no method has been known so far for effectively utilizing branches and leaves.
It is known that smokes containing various chemicals such as nitrogen oxides (NOx) and sulfur oxides (SOx) are discharged from boilers operated in power stations and plants and refuse incinerator sites. It is also known that automobile exhausts contain various chemicals harmful to humans, in particular, NOx and SOx.
These NOx and SOx are not only harmful to humans but also cause acid rainfall. Furthermore, photochemical reactions induced by solar light in the coexistence of NOx and non-methane hydrocarbons cause photochemical smog. Photochemical smog is a phenomenon caused by hydrocarbons and NOx in atmosphere which absorb ultraviolet light and undergo photochemical reactions to form harmful photochemical oxidants and the like. However, the delay in countermeasures against NOx, in particular, NOx discharged from mobile sources such as automobiles has brought about serious problems.
It is also known that various volatile organic solvents are used in interior materials such as wall papers and these VOCs (volatile organic compounds) volatilize indoors. That is, adhesives are widely used in architectural materials and furniture employed for building houses and constructing internal equipments. It is known that, as these adhesives, urea resin-based adhesives, melamine/urea co-condensation resin-based adhesives, phenolic resin-based adhesives and the like are frequently employed from the stand points of performance, cost and convenience. These adhesives, which contain formaldehyde employed as one of starting materials and therefore also called formaldehyde-type adhesives, release formaldehyde into atmosphere.
For example, a urea resin-based adhesive as described above cures through the formation of methylol group by an addition reaction of formaldehyde followed by the formation of methylene bond and dimethylene-ether bond by condensation. Formaldehyde is released not only in the course of the curing as described above but also from the cured adhesive. Namely, deformaldehyde accompanies the progress of the decomposition of the methylol group and the condensation of the dimethylene-ether bond to the methylene bond. Accordingly, formaldehyde is continuously released from the cured urea resin-based adhesive over a long period of time. The same phenomenon is observed in many other adhesives excluding phenolic resins which scarcely release formaldehyde.
Concerning methods for removing these environmental pollutants such as NOx, SOx and formaldehyde as described above, methods for removing NOx by passing an NOx-containing material through a solution of an absorbent such as a carboxylic acid or an alkali or passing the same through a specific machine have been developed. However, these methods require troublesome procedures and high cost. As another method, Patent Document 1 discloses an agent for removing harmful chemicals which contains, as the active ingredient, an aqueous solution containing plant essential oil containing an essential oil obtained by steam-distilling a plant, a water-soluble fraction obtained in the steam distillation and water. Patent Document 2 discloses a method for removing NOx, which includes gasifying a terpene compound having conjugated double bond such as α-terpinene, myrcene or alloocimen and dispersing the same into the air so as to include NOx contained in the air into the terpene compound.
Concerning formaldehyde, the present inventors disclose a method for capturing formaldehyde, containing: (a) a step for sucking formaldehyde-containing air into a first container and bringing the air into contact with complex volatile aroma components, having been extracted from tree leaves, in the container to thereby capture formaldehyde; (b) the step for removing ozone from the air having been treated in the above step; and (c) a step for bringing the air, from which ozone has been removed, into contact with silica gel coated with 2,4-dinitrophenylhydrazine to thereby further capture formaldehyde in the gas (Patent Document 3).
Although distillate components obtained by steam distillation are used in all of the methods of Patent Documents 1, 2 and 3, such substances obtained by steam distillation contain a large amount of irritating smell-generating components such as phenol. Therefore, these substances cannot be dispersed directly into atmosphere. Before dispersing into atmosphere, these substances should be purified to remove the aforesaid irritating components. Such purification causes an additional cost and, therefore, brings about an economical problem.
It is known that plant leaves contain terpene compounds. Application of these terpene compounds to the final removal of environmental pollutants, if possible, contributes to the effective utilization of branches and leaves obtained by tree thinning and pruning as a resource. However, no means therefor has been known so far.